(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)

June 18, 2018

(Date
of Event Which Requires Filing of This Statement)

If the filing
person has previously filed a statement on Schedule 13G to report the acquisition which is the subject of this Schedule 13D, and is filing this schedule because of Rule 13d-1(e),13d-1(f) or 13d-1(g), check the following box. ☐

*

The remainder of this cover page shall be filled out for a reporting persons initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information
which would alter disclosures provided in a prior cover page.

The information required on the remainder of this cover page
shall not be deemed to be filed for the purpose of Section 18 of the Securities Exchange Act of 1934 (Act) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other
provisions of the Act (however, see the Notes).

(Continued on following pages)

(Page 1 of 15 Pages)

Class A CUSIP Number: 25659T107

Class B CUSIP Number: Not Applicable

Page
2
of 15 Pages

1.

Names of
reporting persons

Dagmar Dolby

2.

Check the appropriate box if a member
of a group (see instructions)

(a) ☐ (b) ☐

3.

SEC use only

4.

Source of funds (see instructions)

Not applicable

5.

Check if disclosure of legal
proceedings is required pursuant to Items 2(d) or 2(e) ☐

6.

Citizenship or place of
organization

USA

Number of

shares

beneficially

owned by

each

reporting

person

with

7.

Sole voting power

793,164 shares of Class A Common Stock (1)(2)

8.

Shared voting power

1,126,000 shares of Class A Common Stock and 32,788,779 shares of Class B
Common Stock (1)(3)

9.

Sole dispositive power

793,164 shares of Class A Common Stock and 39,776,233 shares of Class B
Common Stock (1)(4)

10.

Shared dispositive power

126,000 shares of Class A Common Stock
(1)(5)

11.

Aggregate amount beneficially owned by each reporting person

1,919,164 shares of Class A Common Stock and 39,776,233 shares of Class B Common Stock (1)(3)(4)

The rights of the holders of Class A Common Stock and Class B Common Stock are identical, except with respect to conversion rights and voting rights. Each share of Class B Common Stock is convertible into
one share of Class A Common Stock, at no cost, at any time at the option of the holder, upon the affirmative vote of the holders of a majority of the shares of Class B Common Stock, or upon certain transfers. Each share of Class B
Common Stock is entitled to ten votes per share, whereas each share of Class A Common Stock is entitled to one vote per share.

(2)

Consists of 793,164 shares of Class A Common Stock held of record by the Ray and Dagmar Dolby Family Fund, a California nonprofit public benefit corporation and a private foundation within the meaning of section
509(a) of the Internal Revenue Code (the Dolby Family Fund). Dagmar Dolby is the President and sole director of, and has sole dispositive and voting power over the shares held of record by, the Dolby Family Fund. The
Reporting Person disclaims beneficial ownership of these securities except to the extent of her pecuniary interest therein.

(3)

Consists of (i) 1,126,000 shares of Class A Common Stock held of record by the Dagmar Dolby Fund, a California nonprofit public benefit corporation (the Dagmar Dolby Fund),
(ii) 24,108,162 shares of Class B Common Stock held of record by Dagmar Dolby, as Trustee of the Marital Trust under the Dolby Family Trust Instrument dated May 7, 1999 (the Marital Trust), and
(iii) 8,680,617 shares of Class B Common Stock held of record by Dagmar Dolby, as Trustee of the Dagmar Dolby Trust under the Dolby Family Trust Instrument dated May 7, 1999 (the Dagmar Dolby Trust). Dagmar
Dolby, as one of three directors of the Dagmar Dolby Fund, has shared voting power over all 1,126,000 shares of Class A Common Stock held of record by the Dagmar Dolby Fund and has or will have within 60 days after June 20, 2018 shared
dispositive power over 126,000 of the shares of Class A Common Stock held of record by the Dagmar Dolby Fund, with voting and disposition decisions regarding such shares requiring the majority vote of the Dagmar Dolby Funds board of
directors. David E. Dolby, Dagmar Dolbys son, is the Special Trustee of each of the Marital Trust and the Dagmar Dolby Trust. Dagmar Dolby has sole dispositive power over the shares held of record by each of the Marital Trust and the Dagmar
Dolby Trust, and Dagmar Dolby and David E. Dolby have shared voting power over the shares held of record by each of the Marital Trust and the Dagmar Dolby Trust, with voting decisions requiring the unanimous vote of the Trustee and the Special
Trustee. The Reporting Person disclaims beneficial ownership of these securities except to the extent of her pecuniary interest therein.

(4)

Consists of (i) 793,164 shares of Class A Common Stock held of record by the Dolby Family Fund, (ii) 24,108,162 shares of Class B Common Stock held of record by Dagmar Dolby, as Trustee of the
Marital Trust, (iii) 8,680,617 shares of Class B Common Stock held of record by Dagmar Dolby, as Trustee of the Dagmar Dolby Trust, (iv) 160,592 shares of Class B Common Stock held of record by Dagmar Dolby, as Trustee of the Ray
Dolby 2002 Trust A dated April 19, 2002 (the Ray Dolby 2002 Trust A), (v) 463,262 shares of Class B Common Stock held of record by Dagmar Dolby, as Trustee of the Ray Dolby 2002 Trust B dated
April 19, 2002 (the Ray Dolby 2002 Trust B), (vi) 1,040,000 shares of Class B Common Stock held of record by Dolby Holdings II LLC (Dolby
Holdings II), (vii) 350,000 shares of Class B Common Stock held of record by Dolby Holdings III LLC (Dolby Holdings III), (viii) 1,173,600 shares of Class B
Common Stock held of record by Dagmar Dolby, as Trustee of the Dagmar Dolby 2017 Trust BB dated May 25, 2017 (the Dagmar Dolby 2017 Trust BB), and (ix) 3,800,000 shares of Class B Common
Stock held of record by Dagmar Dolby, as Trustee of the Dagmar Dolby 2018 Trust BB dated June 20, 2018 (the Dagmar Dolby 2018 Trust BB). Dagmar Dolby is the Trustee of, and has sole dispositive power
over the shares held of record by, each of the Marital Trust, the Dagmar Dolby Trust, the Ray Dolby 2002 Trust A, the Ray Dolby 2002 Trust B, the Dagmar Dolby 2017 Trust BB and the Dagmar Dolby 2018 Trust BB. Dagmar Dolby and David E. Dolby, Special
Trustee of the Marital Trust and the Dagmar Dolby Trust, have shared voting power over the shares held of record by each of the Marital Trust and the Dagmar Dolby Trust, with voting decisions requiring the unanimous vote of the Trustee and the
Special Trustee. Thomas E. Dolby, Dagmar Dolbys son, is the Special Trustee of, and has sole voting power over the shares held of record by, the Ray Dolby 2002 Trust A. David E. Dolby is the Special Trustee of, and has sole voting power over
the shares held of record by, each of the Ray Dolby 2002 Trust B, the Dagmar Dolby 2017 Trust BB and the Dagmar Dolby 2018 Trust BB. Dagmar Dolby has sole dispositive power over the shares held of record by Dolby Holdings II and Dolby
Holdings III as the Manager of each, each of Thomas E. Dolby and David E. Dolby has sole voting power over 50% of the shares held of record by Dolby Holdings II as a Special Manager of Dolby Holdings II, and David E. Dolby has sole
voting power over all of the shares held of record by Dolby Holdings III as a Special Manager of Dolby Holdings III. Dagmar Dolby, as the President and sole director of the Dolby Family Fund, has sole dispositive and voting power over the
shares held of record by the Dolby Family Fund. The Reporting Person disclaims beneficial ownership of these securities except to the extent of her pecuniary interest therein.

(5)

Consists of 126,000 shares of Class A Common Stock held of record by the Dagmar Dolby Fund. Dagmar Dolby, as one of three directors of the Dagmar Dolby Fund, has shared voting power over all 1,126,000 shares of
Class A Common Stock held of record by the Dagmar Dolby Fund and has or will have within 60 days after June 20, 2018 shared dispositive power over 126,000 of the shares of Class A Common Stock held of record by the Dagmar Dolby Fund,
with voting and disposition decisions regarding such shares requiring the majority vote of the Dagmar Dolby Funds board of directors. The Reporting Person disclaims beneficial ownership of these securities except to the extent of her pecuniary
interest therein.

(6)

Represents the percentage ownership of Class A Common Stock assuming the conversion of all outstanding shares of Class B Common Stock into shares of Class A Common Stock. The percentage ownership of
Class A Common Stock assuming the conversion of only the outstanding shares of Class B Common Stock beneficially owned by Dagmar Dolby is 40.8%. Dagmar Dolbys percentage ownership of Class B Common Stock is 95.4%.

(7)

The shares represented in Row 11 represent 83.4% of the total outstanding voting power of the Class A Common Stock and Class B Common Stock and the shares over which Dagmar Dolby has sole or shared voting
power represent 68.8% of the total outstanding voting power of the Class A Common Stock and Class B Common Stock.

(8)

Based on 62,434,488 shares of Class A Common Stock and 41,677,918 shares of Class B Common Stock outstanding on April 27, 2018.

Class A CUSIP Number: 25659T107

Class B CUSIP Number: Not Applicable

Page
3
of 15 Pages

1.

Names of
reporting persons

Dagmar Dolby, as Trustee of the Marital Trust under the Dolby
Family Trust Instrument dated May 7, 1999

2.

Check the appropriate box if a member
of a group (see instructions)

(a) ☐ (b) ☐

3.

SEC use only

4.

Source of funds (see instructions)

Not applicable

5.

Check if disclosure of legal
proceedings is required pursuant to Items 2(d) or 2(e) ☐

The rights of the holders of Class A Common Stock and Class B Common Stock are identical, except with respect to conversion rights and voting rights. Each share of Class B Common Stock is convertible into
one share of Class A Common Stock, at no cost, at any time at the option of the holder, upon the affirmative vote of the holders of a majority of the shares of Class B Common Stock, or upon certain transfers. Each share of Class B
Common Stock is entitled to ten votes per share, whereas each share of Class A Common Stock is entitled to one vote per share.

(10)

Consists of 24,108,162 shares of Class B Common Stock held of record by Dagmar Dolby, as Trustee of the Marital Trust. David E. Dolby, Dagmar Dolbys son, is the Special Trustee of the Marital Trust. Dagmar
Dolby has sole dispositive power over the shares held of record by the Marital Trust, and Dagmar Dolby and David E. Dolby have shared voting power over the shares held of record by the Marital Trust, with voting decisions requiring the unanimous
vote of the Trustee and the Special Trustee.

(11)

Represents the percentage ownership of Class A Common Stock assuming the conversion of all outstanding shares of Class B Common Stock into shares of Class A Common Stock. The percentage ownership of
Class A Common Stock assuming the conversion of only the outstanding shares of Class B Common Stock beneficially owned by the Marital Trust is 27.9%. The Marital Trusts percentage ownership of Class B Common Stock is 57.8%.

(12)

Represents 50.3% of the total outstanding voting power of the Class A Common Stock and Class B Common Stock.

(13)

Based on 62,434,488 shares of Class A Common Stock and 41,677,918 shares of Class B Common Stock outstanding on April 27, 2018.

Class A CUSIP Number: 25659T107

Class B CUSIP Number: Not Applicable

Page
4
of 15 Pages

1.

Names of
reporting persons

Dagmar Dolby, as Trustee of the Dagmar Dolby Trust under the
Dolby Family Trust Instrument dated May 7, 1999

2.

Check the appropriate box if a member
of a group (see instructions)

(a) ☐ (b) ☐

3.

SEC use only

4.

Source of funds (see instructions)

Not applicable

5.

Check if disclosure of legal
proceedings is required pursuant to Items 2(d) or 2(e) ☐

The rights of the holders of Class A Common Stock and Class B Common Stock are identical, except with respect to conversion rights and voting rights. Each share of Class B Common Stock is convertible into
one share of Class A Common Stock, at no cost, at any time at the option of the holder, upon the affirmative vote of the holders of a majority of the shares of Class B Common Stock, or upon certain transfers. Each share of Class B
Common Stock is entitled to ten votes per share, whereas each share of Class A Common Stock is entitled to one vote per share.

(15)

Consists of 8,680,617 shares of Class B Common Stock held of record by Dagmar Dolby, as Trustee of the Dagmar Dolby Trust. David E. Dolby, Dagmar Dolbys son, is the Special Trustee of the Dagmar Dolby Trust.
Dagmar Dolby has sole dispositive power over the shares held of record by the Dagmar Dolby Trust, and Dagmar Dolby and David E. Dolby have shared voting power over the shares held of record by the Dagmar Dolby Trust, with voting decisions requiring
the unanimous vote of the Trustee and the Special Trustee.

(16)

Represents the percentage ownership of Class A Common Stock assuming the conversion of all outstanding shares of Class B Common Stock into shares of Class A Common Stock. The percentage ownership of
Class A Common Stock assuming the conversion of only the outstanding shares of Class B Common Stock beneficially owned by the Dagmar Dolby Trust is 12.2%. The Dagmar Dolby Trusts percentage ownership of Class B Common Stock is
20.8%.

(17)

Represents 18.1% of the total outstanding voting power of the Class A Common Stock and Class B Common Stock.

(18)

Based on 62,434,488 shares of Class A Common Stock and 41,677,918 shares of Class B Common Stock outstanding on April 27, 2018.

Class A CUSIP Number: 25659T107

Class B CUSIP Number: Not Applicable

Page
5
of 15 Pages

1.

Names of
reporting persons

Dagmar Dolby, as Trustee of the Ray Dolby 2002 Trust A dated
April 19, 2002

2.

Check the appropriate box if a member
of a group (see instructions)

(a) ☐ (b) ☐

3.

SEC use only

4.

Source of funds (see instructions)

Not applicable

5.

Check if disclosure of legal
proceedings is required pursuant to Items 2(d) or 2(e) ☐

The rights of the holders of Class A Common Stock and Class B Common Stock are identical, except with respect to conversion rights and voting rights. Each share of Class B Common Stock is convertible into
one share of Class A Common Stock, at no cost, at any time at the option of the holder, upon the affirmative vote of the holders of a majority of the shares of Class B Common Stock, or upon certain transfers. Each share of Class B
Common Stock is entitled to ten votes per share, whereas each share of Class A Common Stock is entitled to one vote per share.

(20)

Consists of 160,592 shares of Class B Common Stock held of record by Dagmar Dolby, as Trustee of the Ray Dolby 2002 Trust A. Thomas E. Dolby, Dagmar Dolbys son, is the Special Trustee of the Ray Dolby 2002
Trust A. Dagmar Dolby has sole dispositive power over the shares held of record by the Ray Dolby 2002 Trust A, and Thomas E. Dolby has sole voting power over the shares held of record by the Ray Dolby 2002 Trust A.

(21)

Represents the percentage ownership of Class A Common Stock assuming the conversion of all outstanding shares of Class B Common Stock into shares of Class A Common Stock. The percentage ownership of
Class A Common Stock assuming the conversion of only the outstanding shares of Class B Common Stock beneficially owned by the Ray Dolby 2002 Trust A is 0.3%. The Ray Dolby 2002 Trust As percentage ownership of Class B Common
Stock is 0.4%.

(22)

Represents 0.3% of the total outstanding voting power of the Class A Common Stock and Class B Common Stock.

(23)

Based on 62,434,488 shares of Class A Common Stock and 41,677,918 shares of Class B Common Stock outstanding on April 27, 2018.

The rights of the holders of Class A Common Stock and Class B Common Stock are identical, except with respect to conversion rights and voting rights. Each share of Class B Common Stock is convertible into
one share of Class A Common Stock, at no cost, at any time at the option of the holder, upon the affirmative vote of the holders of a majority of the shares of Class B Common Stock, or upon certain transfers. Each share of Class B
Common Stock is entitled to ten votes per share, whereas each share of Class A Common Stock is entitled to one vote per share.

(25)

Consists of 463,262 shares of Class B Common Stock held of record by Dagmar Dolby, as Trustee of the Ray Dolby 2002 Trust B. David E. Dolby, Dagmar Dolbys son, is the Special Trustee of the Ray Dolby 2002
Trust B. Dagmar Dolby has sole dispositive power over the shares held of record by the Ray Dolby 2002 Trust B, and David E. Dolby has sole voting power over the shares held of record by the Ray Dolby 2002 Trust B.

(26)

Represents the percentage ownership of Class A Common Stock assuming the conversion of all outstanding shares of Class B Common Stock into shares of Class A Common Stock. The percentage ownership of
Class A Common Stock assuming the conversion of only the outstanding shares of Class B Common Stock beneficially owned by the Ray Dolby 2002 Trust B is 0.7%. The Ray Dolby 2002 Trust Bs percentage ownership of Class B Common
Stock is 1.1%.

(27)

Represents 1.0% of the total outstanding voting power of the Class A Common Stock and Class B Common Stock.

(28)

Based on 62,434,488 shares of Class A Common Stock and 41,677,918 shares of Class B Common Stock outstanding on April 27, 2018.

Class A CUSIP Number: 25659T107

Class B CUSIP Number: Not Applicable

Page
7
of 15 Pages

1.

Names of
reporting persons

Dolby Holdings II LLC

2.

Check the appropriate box if a member
of a group (see instructions)

(a) ☐ (b) ☐

3.

SEC use only

4.

Source of funds (see instructions)

Not applicable

5.

Check if disclosure of legal
proceedings is required pursuant to Items 2(d) or 2(e) ☐

The rights of the holders of Class A Common Stock and Class B Common Stock are identical, except with respect to conversion rights and voting rights. Each share of Class B Common Stock is convertible into
one share of Class A Common Stock, at no cost, at any time at the option of the holder, upon the affirmative vote of the holders of a majority of the shares of Class B Common Stock, or upon certain transfers. Each share of Class B
Common Stock is entitled to ten votes per share, whereas each share of Class A Common Stock is entitled to one vote per share.

(30)

Consists of 1,040,000 shares of Class B Common Stock held of record by Dolby Holdings II. Dagmar Dolby has sole dispositive power over the shares held of record by Dolby Holdings II as the Manager of
Dolby Holdings II. Each of Thomas E. Dolby and David E. Dolby, Dagmar Dolbys sons, has sole voting power over 50% of the shares held of record by Dolby Holdings II as a Special Manager of Dolby Holdings II.

(31)

Represents the percentage ownership of Class A Common Stock assuming the conversion of all outstanding shares of Class B Common Stock into shares of Class A Common Stock. The percentage ownership of
Class A Common Stock assuming the conversion of only the outstanding shares of Class B Common Stock beneficially owned by Dolby Holdings II is 1.6%. Dolby Holdings IIs percentage ownership of Class B Common Stock is
2.5%.

(32)

Represents 2.2% of the total outstanding voting power of the Class A Common Stock and Class B Common Stock.

(33)

Based on 62,434,488 shares of Class A Common Stock and 41,677,918 shares of Class B Common Stock outstanding on April 27, 2018.

Class A CUSIP Number: 25659T107

Class B CUSIP Number: Not Applicable

Page
8
of 15 Pages

1.

Names of
reporting persons

Dolby Holdings III LLC

2.

Check the appropriate box if a member
of a group (see instructions)

(a) ☐ (b) ☐

3.

SEC use only

4.

Source of funds (see instructions)

Not applicable

5.

Check if disclosure of legal
proceedings is required pursuant to Items 2(d) or 2(e) ☐

The rights of the holders of Class A Common Stock and Class B Common Stock are identical, except with respect to conversion rights and voting rights. Each share of Class B Common Stock is convertible into
one share of Class A Common Stock, at no cost, at any time at the option of the holder, upon the affirmative vote of the holders of a majority of the shares of Class B Common Stock, or upon certain transfers. Each share of Class B
Common Stock is entitled to ten votes per share, whereas each share of Class A Common Stock is entitled to one vote per share.

(35)

Consists of 350,000 shares of Class B Common Stock held of record by Dolby Holdings III. Dagmar Dolby has sole dispositive power over the shares held of record by Dolby Holdings III as the Manager of
Dolby Holdings III. David E. Dolby, Dagmar Dolbys son, has sole voting power over the shares held of record by Dolby Holdings III as the Special Manager of Dolby Holdings III.

(36)

Represents the percentage ownership of Class A Common Stock assuming the conversion of all outstanding shares of Class B Common Stock into shares of Class A Common Stock. The percentage ownership of
Class A Common Stock assuming the conversion of only the outstanding shares of Class B Common Stock beneficially owned by Dolby Holdings III is 0.6%. Dolby Holdings IIIs percentage ownership of Class B Common Stock is
0.8%.

(37)

Represents 0.7% of the total outstanding voting power of the Class A Common Stock and Class B Common Stock.

(38)

Based on 62,434,488 shares of Class A Common Stock and 41,677,918 shares of Class B Common Stock outstanding on April 27, 2018.

The rights of the holders of Class A Common Stock and Class B Common Stock are identical, except with respect to conversion rights and voting rights. Each share of Class B Common Stock is convertible into
one share of Class A Common Stock, at no cost, at any time at the option of the holder, upon the affirmative vote of the holders of a majority of the shares of Class B Common Stock, or upon certain transfers. Each share of Class B
Common Stock is entitled to ten votes per share, whereas each share of Class A Common Stock is entitled to one vote per share.

(40)

Consists of 1,173,600 shares of Class B Common Stock held of record by Dagmar Dolby, as Trustee of the Dagmar Dolby 2017 Trust BB. David E. Dolby, Dagmar Dolbys son, is the Special Trustee of the Dagmar Dolby
2017 Trust BB. Dagmar Dolby has sole dispositive power over the shares held of record by the Dagmar Dolby 2017 Trust BB, and David E. Dolby has sole voting power over the shares held of record by the Dagmar Dolby 2017 Trust BB.

(41)

Represents the percentage ownership of Class A Common Stock assuming the conversion of all outstanding shares of Class B Common Stock into shares of Class A Common Stock. The percentage ownership of
Class A Common Stock assuming the conversion of only the outstanding shares of Class B Common Stock beneficially owned by the Dagmar Dolby 2017 Trust BB is 1.8%. The Dagmar Dolby 2017 Trust BBs percentage ownership of Class B
Common Stock is 2.8%.

(42)

Represents 2.4% of the total outstanding voting power of the Class A Common Stock and Class B Common Stock.

(43)

Based on 62,434,488 shares of Class A Common Stock and 41,677,918 shares of Class B Common Stock outstanding on April 27, 2018.

The rights of the holders of Class A Common Stock and Class B Common Stock are identical, except with respect to conversion rights and voting rights. Each share of Class B Common Stock is convertible into
one share of Class A Common Stock, at no cost, at any time at the option of the holder, upon the affirmative vote of the holders of a majority of the shares of Class B Common Stock, or upon certain transfers. Each share of Class B
Common Stock is entitled to ten votes per share, whereas each share of Class A Common Stock is entitled to one vote per share.

(45)

Consists of 3,800,000 shares of Class B Common Stock held of record by Dagmar Dolby, as Trustee of the Dagmar Dolby 2018 Trust BB. David E. Dolby, Dagmar Dolbys son, is the Special Trustee of the Dagmar Dolby
2018 Trust BB. Dagmar Dolby has sole dispositive power over the shares held of record by the Dagmar Dolby 2018 Trust BB, and David E. Dolby has sole voting power over the shares held of record by the Dagmar Dolby 2018 Trust BB.

(46)

Represents the percentage ownership of Class A Common Stock assuming the conversion of all outstanding shares of Class B Common Stock into shares of Class A Common Stock. The percentage ownership of
Class A Common Stock assuming the conversion of only the outstanding shares of Class B Common Stock beneficially owned by the Dagmar Dolby 2018 Trust BB is 5.7%. The Dagmar Dolby 2018 Trust BBs percentage ownership of Class B
Common Stock is 9.1%.

(47)

Represents 7.9% of the total outstanding voting power of the Class A Common Stock and Class B Common Stock.

(48)

Based on 62,434,488 shares of Class A Common Stock and 41,677,918 shares of Class B Common Stock outstanding on April 27, 2018.

Class A CUSIP Number: 25659T107

Class B CUSIP Number: Not Applicable

Page
11
of 15 Pages

1.

Names of
reporting persons

Thomas E. Dolby

2.

Check the appropriate box if a member
of a group (see instructions)

(a) ☐ (b) ☐

3.

SEC use only

4.

Source of funds (see instructions)

Not applicable

5.

Check if disclosure of legal
proceedings is required pursuant to Items 2(d) or 2(e) ☐

The rights of the holders of Class A Common Stock and Class B Common Stock are identical, except with respect to conversion rights and voting rights. Each share of Class B Common Stock is convertible into
one share of Class A Common Stock, at no cost, at any time at the option of the holder, upon the affirmative vote of the holders of a majority of the shares of Class B Common Stock, or upon certain transfers. Each share of Class B
Common Stock is entitled to ten votes per share, whereas each share of Class A Common Stock is entitled to one vote per share.

(50)

Consists of (i) 160,592 shares of Class B Common Stock held of record by Dagmar Dolby, as Trustee of the Ray Dolby 2002 Trust A, and (ii) 520,000 shares of Class B Common Stock held of record by
Dolby Holdings II. Dagmar Dolby, Thomas E. Dolbys mother, is the Trustee of, and has sole dispositive power over the shares held of record by, the Ray Dolby 2002 Trust A. Thomas E. Dolby is the Special Trustee of, and has sole voting
power over the shares held of record by, the Ray Dolby 2002 Trust A. Dagmar Dolby has sole dispositive power over the shares held of record by Dolby Holdings II as the Manager of Dolby Holdings II, and Thomas E. Dolby has sole voting power
over 50% of the 1,040,000 shares of Class B Common Stock held of record by Dolby Holdings II as a Special Manager of Dolby Holdings II. The Reporting Person disclaims beneficial ownership of these securities except to the extent of
his pecuniary interest therein.

(51)

Represents the percentage ownership of Class A Common Stock assuming the conversion of all outstanding shares of Class B Common Stock into shares of Class A Common Stock. The percentage ownership of
Class A Common Stock assuming the conversion of only the outstanding shares of Class B Common Stock beneficially owned by Thomas E. Dolby is 1.1%. Thomas E. Dolbys percentage ownership of Class B Common Stock is 1.6%.

(52)

Represents 1.4% of the total outstanding voting power of the Class A Common Stock and Class B Common Stock.

(53)

Based on 62,434,488 shares of Class A Common Stock and 41,677,918 shares of Class B Common Stock outstanding on April 27, 2018.

Class A CUSIP Number: 25659T107

Class B CUSIP Number: Not Applicable

Page
12
of 15 Pages

1.

Names of
reporting persons

David E. Dolby

2.

Check the appropriate box if a member
of a group (see instructions)

(a) ☐ (b) ☐

3.

SEC use only

4.

Source of funds (see instructions)

Not applicable

5.

Check if disclosure of legal
proceedings is required pursuant to Items 2(d) or 2(e) ☐

6.

Citizenship or place of
organization

USA

Number of

shares

beneficially

owned by

each

reporting

person

with

7.

Sole voting power

62,435 shares of Class A Common Stock and 6,306,862 shares of Class B Common
Stock (54)(55)

8.

Shared voting power

32,788,779 shares of Class B Common Stock (54)(56)

9.

Sole dispositive power

62,435 shares of Class A Common Stock (54)(57)

10.

Shared dispositive power

None

11.

Aggregate amount beneficially owned by each reporting person

62,435 shares of Class A Common Stock and 39,095,641 shares of Class B Common Stock (54)(55)(56)

The rights of the holders of Class A Common Stock and Class B Common Stock are identical, except with respect to conversion rights and voting rights. Each share of Class B Common Stock is convertible into
one share of Class A Common Stock, at no cost, at any time at the option of the holder, upon the affirmative vote of the holders of a majority of the shares of Class B Common Stock, or upon certain transfers. Each share of Class B
Common Stock is entitled to ten votes per share, whereas each share of Class A Common Stock is entitled to one vote per share.

(55)

Consists of (i) 61,150 shares of Class A Common Stock held of record by David E. Dolby, (ii) stock options held of record by David E. Dolby to purchase up to 1,285 shares of Class A Common Stock that
are exercisable within 60 days after June 20, 2018, (iii) 463,262 shares of Class B Common Stock held of record by Dagmar Dolby, as Trustee of the Ray Dolby 2002 Trust B, (iv) 520,000 shares of Class B Common Stock held
of record by Dolby Holdings II, (v) 350,000 shares of Class B Common Stock held of record by Dolby Holdings III, (vi) 1,173,600 shares of Class B Common Stock held of record by Dagmar Dolby, as Trustee of the Dagmar
Dolby 2017 Trust BB, and (vii) 3,800,000 shares of Class B Common Stock held of record by Dagmar Dolby, as Trustee of the Dagmar Dolby 2018 Trust BB. Dagmar Dolby, David E. Dolbys mother, is the Trustee of, and has sole dispositive
power over the shares held of record by, each of the Ray Dolby 2002 Trust B, the Dagmar Dolby 2017 Trust BB and the Dagmar Dolby 2018 Trust BB. David E. Dolby is the Special Trustee of, and has sole voting power over the shares held of record by,
each of the Ray Dolby 2002 Trust B, the Dagmar Dolby 2017 Trust BB and the Dagmar Dolby 2018 Trust BB. Dagmar Dolby has sole dispositive power over the shares held of record by Dolby Holdings II and Dolby Holdings III as the Manager of
each, and David E. Dolby has sole voting power over 50% of the 1,040,000 shares of Class B Common Stock held of record by Dolby Holdings II and all of the 350,000 shares of Class B Common Stock held of record by Dolby
Holdings III, as Special Manager of each. The Reporting Person disclaims beneficial ownership of these securities except to the extent of his pecuniary interest therein.

(56)

Consists of (i) 24,108,162 shares of Class B Common Stock held of record by Dagmar Dolby, as Trustee of the Marital Trust and (ii) 8,680,617 shares of Class B Common Stock held of record by Dagmar
Dolby, as Trustee of the Dagmar Dolby Trust. David E. Dolby is the Special Trustee of each of the Marital Trust and the Dagmar Dolby Trust. Dagmar Dolby has sole dispositive power over the shares held of record by each of the Marital Trust and the
Dagmar Dolby Trust, and Dagmar Dolby and David E. Dolby have shared voting power over the shares held of record by each of the Marital Trust and the Dagmar Dolby Trust, with voting decisions requiring the unanimous vote of the Trustee and the
Special Trustee. The Reporting Person disclaims beneficial ownership of these securities except to the extent of his pecuniary interest therein.

(57)

Consists of (i) 61,150 shares of Class A Common Stock held of record by David E. Dolby, and (ii) stock options held of record by David E. Dolby to purchase up to 1,285 shares of Class A Common Stock
that are exercisable within 60 days after June 20, 2018.

(58)

Represents the percentage ownership of Class A Common Stock assuming the conversion of all outstanding shares of Class B Common Stock into shares of Class A Common Stock. The percentage ownership of
Class A Common Stock assuming the conversion of only the outstanding shares of Class B Common Stock beneficially owned by David E. Dolby is 38.6%. David E. Dolbys percentage ownership of Class B Common Stock is 93.8%.

(59)

Represents 81.6% of the total outstanding voting power of the Class A Common Stock and Class B Common Stock.

(60)

Based on 62,434,488 shares of Class A Common Stock and 41,677,918 shares of Class B Common Stock outstanding on April 27, 2018.

Page
13
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Explanatory Note:

This Amendment No. 40 to Schedule 13D (this Amendment) amends the Schedule 13D initially filed with the Commission
on December 27, 2011 (as subsequently amended prior to the date hereof, the Statement). This Amendment is filed on behalf of (i) Dagmar Dolby, (ii) Thomas E. Dolby, (iii) David E. Dolby, (iv) Dagmar
Dolby, as Trustee of the Marital Trust, (v) Dagmar Dolby, as Trustee of the Dagmar Dolby Trust, (vi) Dagmar Dolby, as Trustee of the Ray Dolby 2002 Trust A, (vii) Dagmar Dolby, as Trustee of the Ray Dolby 2002 Trust B,
(viii) Dolby Holdings II, (ix) Dolby Holdings III, (x) Dagmar Dolby, as Trustee of the Dagmar Dolby 2017 Trust BB, and (xi) Dagmar Dolby, as Trustee of the Dagmar Dolby 2018 Trust BB (collectively,
the Reporting Persons), relating to the beneficial ownership of the Class A Common Stock, $0.001 par value per share (the Class A Common Stock), and the Class B Common
Stock, $0.001 par value per share (the Class B Common Stock), of Dolby Laboratories, Inc., a Delaware corporation (the Company). Except as set forth herein, this Amendment does not
supplement, restate or amend any of the information disclosed in the Statement. Capitalized terms used but not defined in this Amendment have the meanings ascribed to them in the Statement.

Item 2.

Identity and Background.

Item 2 of the Statement is amended and restated in its
entirety to read in full as follows:

Dagmar Dolby is the widow of Ray Dolby, the former Founder and Director Emeritus of the Company, and
serves as the Trustee of each of the Marital Trust, the Dagmar Dolby Trust, the Ray Dolby 2002 Trust A, the Ray Dolby 2002 Trust B, the Dagmar Dolby 2017 Trust BB and the Dagmar Dolby 2018 Trust BB. The Marital Trust and the Dagmar Dolby Trust are
formed under the Dolby Family Trust Instrument dated May 7, 1999, and each such trust was formed for tax and estate planning purposes as a result of the death of Ray Dolby on September 12, 2013. Each of the Dagmar Dolby 2017 Trust BB and
the Dagmar Dolby 2018 Trust BB is a grantor retained annuity trust (GRAT) established by Dagmar Dolby. Dagmar Dolby is a U.S. citizen and each of the Marital Trust, the Dagmar Dolby Trust, the Ray Dolby 2002 Trust A, the Ray Dolby
2002 Trust B, the Dagmar Dolby 2017 Trust BB and the Dagmar Dolby 2018 Trust BB is established under the laws of the State of California.

Thomas E. Dolby, Dagmar Dolbys son, is a writer and serves as the Special Trustee of, and has sole voting power over the shares held of
record by, the Ray Dolby 2002 Trust A.

David E. Dolby, Dagmar Dolbys son, is a director of the Company and serves as a Managing
Director of Dolby Family Ventures, an early-stage venture firm not affiliated with the Company. David E. Dolby serves as the Special Trustee of, and shares voting power with Dagmar Dolby as to the shares held of record by, each of the Marital Trust
and the Dagmar Dolby Trust. David E. Dolby serves as the Special Trustee of, and has sole voting power over the shares held of record by, each of the Ray Dolby 2002 Trust B, the Dagmar Dolby 2017 Trust BB and the Dagmar Dolby 2018 Trust BB.

Each of Dolby Holdings II and Dolby Holdings III (each, a Family LLC) is a limited
liability company formed under the laws of the State of Delaware. Dagmar Dolby is the Manager of each Family LLC; Thomas E. Dolby and David E. Dolby are Special Managers of Dolby Holdings II; and David E. Dolby is the Special Manager of
Dolby Holdings III. The members of the Family LLCs (the Members), which have no management control over the Family LLCs, consist of trusts of which Dagmar Dolby is the trustee that have been established for the
benefit of Dagmar Dolby and/or her immediate family members.

The business address of each of the Reporting Persons and the Members is C/O
Dolby Laboratories, Inc., 1275 Market Street, San Francisco, California 94103.

During the last five years, no Reporting Person or Member
(i) has been convicted in a criminal proceeding (excluding traffic violations or similar misdemeanors), or (ii) has been a party to a civil proceeding of a judicial or administrative body of competent jurisdiction and as a result of such
proceeding was or is subject to a judgment, decree or final order enjoining future violations of, or prohibiting or mandating activities subject to, federal or state securities laws or finding any violations with respect to such laws.

Item 4.

Purpose of Transaction.

Item 4 of the Statement is amended by adding the following
thereto:

On June 20, 2018, the Dagmar Dolby 2017 Trust BB transferred 764,000 shares of Class B Common Stock to the Dagmar
Dolby Trust (the 2017 GRAT 2018 Annuity Share Distribution). The Dagmar Dolby 2017 Trust BBs trust instrument requires an annual annuity payment to the Dagmar Dolby Trust, and the 2017 GRAT 2018 Annuity Share
Distribution was effected in satisfaction of the annuity payment requirements, and in accordance with the terms, of such trust instrument. The 2017 GRAT 2018 Annuity Share Distribution was a transfer for no value, without the payment or receipt of
any funds or other consideration by any Reporting Person in exchange therefor.

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14
of 15 Pages

On June 20, 2018, Dagmar Dolby established a new GRAT, the Dagmar Dolby 2018
Trust BB, and the Dagmar Dolby Trust contributed 3,800,000 shares of Class B Common Stock to such GRAT (the 2018 GRAT Share Contribution). The 2018 GRAT Share Contribution was effected solely for tax and estate
planning purposes, and was a transfer for no value without the payment or receipt of any funds or other consideration by any Reporting Person in exchange therefor.

On June 20, 2018, the limited liability company agreement of Dolby Holdings III was amended to (i) establish the position of Special
Manager, which has sole voting power over all of the shares held of record by Dolby Holdings III, and (ii) appoint David E. Dolby to such position (the DH III LLC Agreement Amendment). The DH III LLC Agreement
Amendment was effected solely for tax and estate planning and investment management purposes and for no value, without the payment or receipt of any funds or other consideration by any Reporting Person in exchange therefor.

Item 5.

Interest in Securities of the Issuer.

Subsection (c) and of Item 5 of the
Statement is amended and restated in its entirety to read in full as follows:

(c) The information set forth in Item 4 regarding
the 2017 GRAT 2018 Annuity Share Distribution, the 2018 GRAT Share Contribution and the DH III LLC Agreement Amendment is incorporated herein by reference. In addition to such transactions, the table set forth on Schedule A
reflects all other transactions effected by the Reporting Persons in the classes of securities reported on during the period beginning on June 6, 2018, the day immediately following the date of the last transaction reported in the most recently
filed amendment to this Statement before the date hereof, and ending on June 20, 2018, the date of the last transaction reported in this Amendment. Each transaction set forth on Schedule A represents (i) the
conversion of the applicable number of shares of Class B Common Stock into an equal number of shares of Class A Common Stock, and (ii) the sale of such shares of Class A Common Stock in open market trades pursuant to the 2018
Trading Plans.

Item 6.

Contracts, Arrangements, Understandings or Relationships with Respect to Securities of the Issuer.

Item 6 of the Statement is amended by adding the following thereto:

The information set forth in Item 4 is incorporated herein by reference.

Item 7.

Material to Be Filed as Exhibits.

Exhibit 1:

Joint Filing Agreement pursuant to Rule 13d-1(k)(1) (filed herewith).

Exhibit 2:

Power of Attorney  Dagmar Dolby (incorporated by reference to Exhibit 2 to the Schedule 13D/A filed with the Commission on March 10, 2014).

Exhibit 3:

Power of Attorney  Thomas E. Dolby (incorporated by reference to Exhibit 3 to the Schedule 13D/A filed with the Commission on March 10, 2014).

Exhibit 4:

Power of Attorney  David E. Dolby (incorporated by reference to Exhibit 4 to the Schedule 13D/A filed with the Commission on March 10, 2014).

Exhibit 5:

Power of Attorney  Marital Trust (incorporated by reference to Exhibit 6 to the Schedule 13D/A filed with the Commission on March 10, 2014).

Exhibit 6

Power of Attorney  Dagmar Dolby Trust (incorporated by reference to Exhibit 7 to the Schedule 13D/A filed with the Commission on March 10, 2014).

Exhibit 7:

Power of Attorney  Ray Dolby 2002 Trust A (incorporated by reference to Exhibit 8 to the Schedule 13D/A filed with the Commission on March 10, 2014).

Exhibit 8:

Power of Attorney  Ray Dolby 2002 Trust B (incorporated by reference to Exhibit 9 to the Schedule 13D/A filed with the Commission on March 10, 2014).

Exhibit 9:

Power of Attorney  Dolby Holdings II (incorporated by reference to Exhibit 12 to the Schedule 13D/A filed with the Commission on March 10, 2014).

Exhibit 10:

Power of Attorney  Dolby Holdings III (incorporated by reference to Exhibit 10 to the Schedule 13D/A filed with the Commission on March 29, 2018).

Exhibit 11:

Power of Attorney  Dagmar Dolby 2017 Trust BB (incorporated by reference to Exhibit 11 to the Schedule 13D/A filed with the Commission on May 26, 2017).

Exhibit 12:

Power of Attorney  Dagmar Dolby 2018 Trust BB (filed herewith).

Page
15
of 15 Pages

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this Statement is true,
complete and correct.

Date: June 21, 2018.

DAGMAR DOLBY

MARITAL TRUST UNDER THE DOLBY FAMILY TRUST INSTRUMENT DATED MAY 7, 1999

By:

*

By:

*

Dagmar Dolby

Name: Dagmar Dolby

Title: Trustee

THOMAS E. DOLBY

DAGMAR DOLBY TRUST UNDER THE DOLBY FAMILY TRUST INSTRUMENT DATED MAY 7, 1999

By:

*

By:

*

Thomas E. Dolby

Name: Dagmar Dolby

Title: Trustee

DAVID E. DOLBY

RAY DOLBY 2002 TRUST A DATED APRIL 19, 2002

By:

*

By:

*

David E. Dolby

Name: Dagmar Dolby

Title: Trustee

DAGMAR DOLBY 2017 TRUST BB DATED MAY 25, 2017

RAY DOLBY 2002 TRUST B DATED APRIL 19, 2002

By:

*

By:

*

Name: Dagmar Dolby

Name: Dagmar Dolby

Title: Trustee

Title: Trustee

DAGMAR DOLBY 2018 TRUST BB DATED JUNE 20, 2018

DOLBY HOLDINGS II LLC

By:

*

By:

*

Name: Dagmar Dolby

Name: Dagmar Dolby

Title: Trustee

Title: Manager

DOLBY HOLDINGS III LLC

By:

*

Name: Dagmar Dolby

Title: Manager

*By:

/s/ Patrick McCabe

Patrick McCabe, on behalf of Shartsis Friese LLP,

as Attorney-in-Fact

SCHEDULE A

Name of Reporting Person

Date ofTransaction

No. of Shares

Sale Price PerShare of Class ACommon Stock (1)

Dagmar Dolby Trust

6/6/2018

50,000

$

64.3601

(2)

Dagmar Dolby Trust

6/7/2018

50,000

$

64.4470

(3)

Dagmar Dolby Trust

6/8/2018

50,000

$

64.2501

(4)

Dagmar Dolby Trust

6/11/2018

50,000

$

64.3118

(5)

Dagmar Dolby Trust

6/12/2018

50,000

$

64.0142

(6)

Dagmar Dolby Trust

6/13/2018

50,000

$

64.4979

(7)

Dagmar Dolby Trust

6/14/2018

50,000

$

65.2405

(8)

Dagmar Dolby Trust

6/15/2018

50,000

$

65.1069

(9)

Dagmar Dolby Trust

6/18/2018

50,000

$

65.5035

(10)

Dagmar Dolby Trust

6/19/2018

49,900

$

64.8208

(11)

Dagmar Dolby Trust

6/19/2018

100

$

65.1700

Dagmar Dolby Trust

6/20/2018

50,000

$

65.2182

(12)

(1)

The applicable Reporting Person hereby undertakes to provide upon request to the Commission, the Company or a security holder of the Company full information regarding the number of shares and prices at which the
transactions were effected.

(2)

Reflects the weighted average sale price, for multiple transactions executed at prices ranging from $64.155 to $64.54 per share, inclusive.

(3)

Reflects the weighted average sale price, for multiple transactions executed at prices ranging from $64.255 to $64.69 per share, inclusive.

(4)

Reflects the weighted average sale price, for multiple transactions executed at prices ranging from $63.93 to $64.73 per share, inclusive.

(5)

Reflects the weighted average sale price, for multiple transactions executed at prices ranging from $63.96 to $64.51 per share, inclusive.

(6)

Reflects the weighted average sale price, for multiple transactions executed at prices ranging from $63.54 to $64.46 per share, inclusive.

(7)

Reflects the weighted average sale price, for multiple transactions executed at prices ranging from $64.13 to $64.74 per share, inclusive.

(8)

Reflects the weighted average sale price, for multiple transactions executed at prices ranging from $64.61 to $65.48 per share, inclusive.

(9)

Reflects the weighted average sale price, for multiple transactions executed at prices ranging from $64.66 to $65.39 per share, inclusive.

(10)

Reflects the weighted average sale price, for multiple transactions executed at prices ranging from $64.97 to $65.70 per share, inclusive.

(11)

Reflects the weighted average sale price, for multiple transactions executed at prices ranging from $64.13 to $65.12 per share, inclusive.

(12)

Reflects the weighted average sale price, for multiple transactions executed at prices ranging from $64.915 to $65.35 per share, inclusive.

EX-99.1

Exhibit 1

JOINT FILING AGREEMENT

The undersigned acknowledge and agree that the foregoing statement on Schedule 13D is filed on behalf of each of the undersigned and that all
subsequent amendments to this statement on Schedule 13D shall be filed on behalf of each of the undersigned without the necessity of filing additional joint filing statements. The undersigned acknowledge that each shall be responsible for the timely
filing of such amendments, and for the completeness and accuracy of the information concerning him, her or it contained herein, but shall not be responsible for the completeness and accuracy of the information concerning the other entities or
persons, except to the extent that he, she or it knows or has reason to believe that such information is inaccurate.

Date: June 21,
2018.

DAGMAR DOLBY

MARITAL TRUST UNDER THE DOLBY FAMILY TRUST INSTRUMENT DATED MAY 7, 1999

By:

*

By:

*

Dagmar Dolby

Name: Dagmar Dolby

Title: Trustee

THOMAS E. DOLBY

DAGMAR DOLBY TRUST UNDER THE DOLBY FAMILY TRUST INSTRUMENT DATED MAY 7, 1999

execute for and on behalf of the undersigned statements on Schedule 13D or Schedule 13G, and Forms ID, 3,4 and 5, in accordance with Section 13 or Section 16 of the Securities Exchange Act of 1934, as amended,
and the rules thereunder;

(2)

do and perform any and all acts for and on behalf of the undersigned which may be necessary or desirable to complete and execute any such statement on Schedule 13D or Schedule 13G, or Form ID, 3, 4 or 5, including any
electronic filing thereof, complete and execute any amendment or amendments thereto, and timely file such form with the United States Securities and Exchange Commission and any stock exchange or similar authority; and

(3)

take any other action of any type whatsoever in connection with the foregoing which, in the opinion of such attorney-in-fact, may be of
benefit to, in the best interest of, or legally required by, the undersigned, it being understood that the documents executed by
such attorney-in-fact on behalf of the
undersigned pursuant to this Power of Attorney shall be in such form and shall contain such terms and conditions as such attorney-in-fact may approve in such attorney-in-facts discretion.

The undersigned hereby grants
to each such attorney-in-fact full power and authority to do and perform any and every act and thing whatsoever necessary or proper to be done in the exercise of any of
the rights and powers herein granted, as fully to all intents and purposes as the undersigned might or could do if personally present, with full power of substitution or revocation, hereby ratifying and confirming all that such attorney-in-fact, or such attorney-in-facts substitute or substitutes, shall lawfully do
or cause to be done by virtue of this Power of Attorney and the rights and powers herein granted. The undersigned acknowledges that the foregoing attorneys-in-fact, in
serving in such capacity at the request of the undersigned, are not assuming any of the undersigneds responsibilities to comply with Section 13 or Section 16 of the Securities Exchange Act of 1934, as amended, and the rules
thereunder.

This Power of Attorney shall remain in full force and effect until the undersigned is no longer required to file statements on Schedule 13D
or Schedule 13G, or Form ID, 3, 4 and 5, with respect to the undersigneds holdings of and transactions in securities issued by Dolby Laboratories, Inc., unless earlier revoked by the undersigned in a signed writing delivered to the foregoing attorneys-in-fact.

IN WITNESS WHEREOF, the undersigned has caused this Power of
Attorney to be executed as of June 20, 2018.